I'm using PP CS4 on a Mac OS 10.5.5 computer. I'm having problems playing back a timeline that has multiple layers, effects and overlays (Pre-Render). I have to render to be able to playback smoothly. In CS3 the same projects I could playback fine before I render. The quality would just be lower. Does anybody know if there are playback setting adjustments I can make to make playback smoother? I already tried putting the "program monitor" to draft quality and it helped a little, but not much.
It's possible the conversion from CS3 to CS4 caused the problem. I had a similar experience. You might try taking your footage offline then re-linking and see if that helps. Be aware thought that any multicam sequences will probably get screwed up. You might want to save the project with a new name first.